The PON can be classified as a Broadband Passive Optical Network (BPON), an Ethernet Passive Optical Network (EPON), a Gigabit Passive Optical Network (GPON) and a Wavelength Division Multiplexing Passive Optical Network (WDM-PON), etc. As shown in FIG. 1, the PON includes an Optical Line Terminal (OLT), an Optical Distribution Network (ODN), and Optical Network Units (ONUs)/Optical Network Terminals (ONTs). The OLT acts as an interface of network side or service access node side. The ODN splits one optical signal sourced from the OLT into a number of optical signals and sends the optical signals to the ONUs/ONTs via optical modules downstream, and combines a number of optical signals from the ONUs/ONTs into one optical signal and sends the optical signal to the OLT via optical modules upstream. The ONUs/ONTs, located at user side, convert optical signals into electrical signals and send the electrical signals to user terminals downstream, and convert electrical signals from the user terminals into optical signals and send the optical signals to optical fibers upstream.
In the prior art, the OLT includes a burst mode optical receiver, which is used for correctly receiving burst data from ONUs/ONTs, and the ONU/ONT includes a burst mode optical transmitter, which is used for sending or receiving data in a burst mode responding to the grants assigned by the OLT in accordance with a predetermined scheduling algorithm in the OLT. In the case of sending data by using a burst mode optical module, a laser is only opened to send during the timeslots which are assigned to the ONU/ONT, and should be closed in other timeslots even the ONU/ONT has some data to be sent to OLT. In normal situation, only one laser of an ONU/ONT device can be opened during a timeslot. In this case, the optical power received at a receiving end of the OLT substantively depends on output power of the working laser and loss of the optical fiber links. The advantages of sending and receiving data with the burst mode optical modules are simple implementation and high precision, however, high cost compared with continuous optical modules.
In the prior art, tunable wavelength optical modules are used in the WDM-PON so that distributable fixed wavelengths can be utilized to send data by the optical modules of the ONU/ONT, which improves the utilization efficiency of the optical fibers. However, because the optical wavelengths sent from the ONU/ONT devices are different from each other, multiple optical receivers at the receiving end of OLT should be used to receive optical signals with different wavelengths. Thus, this technique is complex to be implemented. Since optical signals with different wavelengths, which represent different channels, need to be differentiated from each other by the OLT device, high stability of optical wavelengths sent from the ONU/ONT is required, thus high quality of the optical modules of the OLT and ONU/ONT devices is required. Therefore, prices of the optical modules are high, which results in high cost of the whole network.